With growing demands for cloud storage and cloud-based network computing applications, high and ultrahigh data rate recording becomes important for near-line and high-end disk drive devices. It is essential to design a PMR writer that can achieve optimum high data rate performance in both area density capability (ADC) and side track erasure (STE) capability.
A PMR write head typically has a main pole layer with a small surface area at an air bearing surface (ABS), and coils that conduct a current and generate a magnetic flux in the main pole layer such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through a trailing loop comprised of a trailing shield structure with a front side at the ABS and a PP3 trailing shield portion that extends over the write coils and connects to a top surface of the main pole layer above a back gap magnetic connection.
For both conventional (CMR) and shingle magnetic recording (SMR), continuous improvement in storage area density or ADC is required for a PMR writer in order to deliver or pack higher bits per inch (BPI) and higher tracks per inch (TPI). An all wrap around (AWA) shield structure that surrounds the main pole layer in a PMR write head is desirable in that the trailing shield is responsible for improving down track field gradient while side shields and a leading shield improve the cross track field gradient and TPI as well as adjacent track erasure (ATE) performance.
Current PMR writers tend to have the trailing shield (TS) layer in one piece with the same material from center to edge of the trailing shield structure. As depicted in FIG. 1, PMR head performance sits on a line where better TS efficiency (ADC) is typically traded off for better WATE by selecting magnetic materials with different Ms values. With a high Ms material, the magnetic path driving main pole and trailing shield gains efficiency from low reluctance. However, high Ms materials also lead to more field leakage and worse WATE.
Referring to FIG. 2, an ABS view of an AWA shield structure previously disclosed in related U.S. Pat. No. 9,466,319 is depicted. Main pole 14 is shown with a trailing side 14t having track width TW, and the leading side 14b, which contacts lead gap 13 at the ABS. Trailing and leading sides are connected by two sides 14s that each adjoin a side gap 15 with a cross-track width d. Center plane 44-44 bisects the main pole in a down-track direction. Side shields 12 contact a top surface 11t of leading shield 11, and each side shield has a top surface 12t at a plane 41-41 that is orthogonal to the ABS and to the center plane, and includes main pole trailing side 14t at the ABS. Write gap 16 having thickness a, and hot seed (19-24 kG) layer 17, where kG hereinafter is used to denote the saturation magnetic moment in kiloGauss of a layer or material, are sequentially formed on the main pole trailing side and each has a cross-track width w. A full width trailing shield layer 18 made of a 10-19 kG material such as FeNiRe is formed on a top surface of the hot seed layer and along the sides of the write gap and hot seed layer. Trailing shield layer 20 consists of hot seed layer 17 and trailing shield layer 18. A PP3 trailing shield (not shown) is exposed to the ABS, and adjoins a top surface of TS layer 18.
When one or more of the leading shield, side shields, and trailing shield are made of a high damping material, WATE performance is significantly improved without adversely affecting ADC. During dynamic magnetic recording, the high frequency magnetic field generated from the main pole will excite the dynamic magnetization rotation inside all of the surrounding shields. The dynamic magnetization rotations will propagate away from the main pole, and due to complicated domains in the shields including the trailing shield, the resulting magnetization wave may trigger localized magnetic charges that will cause WATE. It is believed that shields made of a high damping magnetic material will significantly reduce the propagation distance of the dynamic magnetization rotation wave due to fast energy dissipation under high damping constant. Hence, localized magnetic charge generation will be minimized in the shield structure thereby reducing the WATE. An improved trailing shield design is needed to escape the tradeoff line in FIG. 1 and approach a point A where both high trailing shield efficiency in terms of improved ADC and clean WATE are realized.